The digestion and assimilation of fat in the human body : an epitome of laboratory notes on physiological and chemical experiments bearing on this subject

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THE

DIGESTIOXAND^ASSIMILATION OF
EAT II THE HUMAN BODY.

AX EPITOME OF LABORATORY NOTES ON

PHYSIOLOGICAL AND CHEMICAL EXPERIMENTS BEARING

ON THIS. SUBJECT.

H. CRITCHETT, BARTLETT, PhJ)., F.C.S.,

AUTHOR OP

ANALYTICAL PAPERS ON THE SUBJECTS OP FOOD AND THE NOURISHMENT OP THE BODY

IN '• THE LANCET," " THE BRITISH MEDICAL JOURNAL,"

"THE MEDICAL PRESS AND CIRCULAR," "THE MEDICAL RECORD,"

"THE SANITARY RECORD," ''PUBLIC HEALTH," ETC.

HEW YORK

LONDON:
J. & A. CHURCHILL, NEW BURLINGTON STREET.

1877.

THE

DIGESTION AND ASSIMILATION OF
FAT IN THE HUMAN BODY.

AN EPITOME OF LABORATORY NOTES ON

PHYSIOLOGICAL AND CHEMICAL EXPERIMENTS BEARING

ON THIS SUBJECT.

H. CRITCHETT, BARTLETT, PhJX, F.C.S.,

AUTHOR OF

ANALYTICAL PAPERS ON THE SUBJECTS OP FOOD AND THE NOURISHMENT OF THE BODT

IN '• THE LANCET," " THE BRITISH MEDICAL JOURNAL,"

" THE MEDICAL PRESS AND CIRCULAR," " THE MEDICAL RECORD,"

" THE SANITARY RECORD," " PUBLIC HEALTH," ETC.

LONDON:

J. & A. CHURCHILL, NEW BURLINGTON STREET.

1877,

6

CONTENTS.

rim

Iktroducthw ... ... ... ... . . # 5

CHAPTER I.

A Brief Account ef the Circumstances, Experiments, and Con-
siderations leading to what is believed to be an Elucidation
of the Digestion and Absorption of Fatty Matters ... 9

Description of some of the Reactions and Functions of Pancreatic

Fluid ... ... ... ... ... ... 10

Analytical Processes for the Separation of the Active Principles

and other Components ... ... ... ... 14

The Fermentative Nature of the Pancreative Principles ... 19

The Emulsifying Power of the Pancreatic Fluid ... ... 22

The Manner in which a New Principle is thought to have been

Detected and Confirmed ... ... ... ... 26

CHAPTER II.

3iology and Che
reliminary Digestion of Fats ... ... ... 29

A Blight Sketch of the Physiology and Chemistry relating to the

CHAPTER III.
The Digestion of Fat in the Small Intestine ... ... 34

CHAPTER IV.
Artificial Aids to the Digestion of Fat ... ... ... 40

ADDENDUM.

Basly Evidence of the Commencement of Wasting Diseases dis-
covered bj the Excretion of Soluble Fat ... - • • *&

THE DIGESTION AND ASSIMILATION OF
FAT IN THE HUMAN BODY.

INTKODUCTION.

Towaeds the autumn of 1872, a somewhat warm con-
troversy sprung up between the late Dr. Edward Smith
and myself, among others, respecting the proportional
nntriment and digestibility of certain articles of preserved
food, particularly in regard to "Australian meat" and
" condensed milk."

The numerous letters which appeared in The Times
and Standard, together with the more elaborate arguments
brought forward in the columns of several scientific
journals, attracted the attention of my esteemed friend
and teacher, Baron von Liebig. A very interesting
correspondence ensued, discussing minutely the various
questions at issue.

Among other valuable results, I may incidentally
mention the final repudiation by Liebig of the untenable
assumption that his own " extr actum carnis " was of a
food value bearing any close relation to the nutriment
contained in the whole bulk of meat from which it had
been extracted. This candid admission of mistaken

6 THE DIGESTION AND ASSIMILATION OF

views, which were previously advanced with no little
firmness and pertinacity, exhibited a great mind rising
superior to every self-interest and prejudice. As a direct
consequence of our intercommunication, this was natu-
rally highly gratifying to me ; but it is as an instructive
example, which may be borne in mind by all scientific
writers, no matter how distinguished then' position, that
siK-h a recantation should be regarded.*

During the progress of the discussion, Liebig expressed
a wish that I should place myself in communication with
Drs. Playfair and Bence Jones. The former was away
from London at the time, and when in town was neces-
sarily absorbed by the cares of high official duties ; I there-
fore invoked the kindly assistance of the secretary of" the
Royal Institution.

Dr. Bence Jones advised that a number of experiments
on the digestion of food should be undertaken ; and, after
much consideration, wrote to me, suggesting the tabula-
tion of a very lengthy series of reactions, only to be at-
tained by a course of investigation extending over several
years.

The various proximate principles of food were to be
administered without any mixture with other matters,
except water. The reactions to be recorded were as to
acidity, neutrality, or alkalinity during each stage of
digestion, from the mouth to the lower bowel. Not only
was the food mass to be thus tested, but my far-seeing
adviser was still more interested in obtaining similar
indications respecting the different conditions of the
various digesting juices. They were to be taken just as

* A precedent so frank was not lost on Dr. Edward Smith, who in his
later writings also virtually admitted that he had entertained erroneous
views even on the main points of the controversy.

HUMAN BODY.

secreted in their respective glands during the digestion of
each single component of food, the like observations being
registered before and after digestional activity. Even
beyond this, it was considered very desirable that the
muscular tissues surrounding the digestive organs should
be equally carefully tested, for reasons which I scarcely
understood the important bearings of at the time.

While the processes of digestion in life were to be
studied to afford the closest possible insight into the
laws which govern the solution and absorption of the
various food principles, the artificial digestion of tingle
components of food, to be afterwards supplemented by
simple combinations, was proposed to be experimented on
in the laboratory with a completeness I have not yet
been able to fully carry out.

Here was a programme ambitious enough, if affording
any promise of leading up to a thorough comprehension
of the true principles of the digestion of food, ho <v ever
complex in their alternations and combinatVns in the
living human economy. Dr. Bence Jon' s .vas tjtiite
persuaded that such a course of experimen s w Duld con-
tribute, at least, to the foundation of sucL I .*ow)edge,
and he was eager to obtain the information to be acquired
by this means.

I have so far quoted from such of his letters as I have
still by me. Whether he would have consider'.":! his
anticipations just ified by the progress since made, ■ can-
not presume to decide; but of this I am fully conscious,
that in losing the benefit of his co-operation, advice, and
encouragement, at his decease in the following year,
many of the immediate scientific deductions logically to
be drawn from the experiments made have been lost for
ever.

8 THE DIGESTION AND ASSIMILATION OF

Unable to devote the whole of my time and the con-
siderable amount of money necessary to carry out the
proposed research in its integrity, and being now
hampered by the recent anti-vivisectional legislation,
it is improbable that I shall be able to complete the
physiological investigations commenced under such
favourable auspices.

Accident, however, conduced to forward one particular
train of experiments, namely, that on the digestion of
fat in the living body ; and as the artificial digestion of
fatty matters was undertaken contemporaneously, the
results have attained a greater advance than in any of
the other sections. I therefore intend to discuss in this
short treatise the general principles of digestion involved,
to that extent only which may be necessary to explain
their bearing in this instance.

For the last eighteen months I have had the valuable
assistance of Dr. G. Overend Drewry, whose collaboration
in the later physiological experiments has very materially
helped to work out some of the more interesting problems
connected with these peculiar digestional phenomena.

FAT IN THE HUMAN BODY.

CHAPTER I.

A BRIEF ACCOUNT OF THE CIRCUMSTANCES, EXPERIMENTS, AND CON-
SIDERATIONS LEADING TO WHAT IS BELIEVED TO BE AN ELUCIDATION
OF THE DIGESTION AND ABSORPTION OF FATTY MATTERS.

The examination of the constituents of the gastric fluids
of the stomach forms naturally a leading feature of the
scheme proposed by Dr. Bence Jones. It was on that
score I was led to attempt the determination as to
whether the solvent power of pepsin upon the albumin-
ous portions of food is, or is not, accelerated and assisted
in its own function by admixture with other digestive
principles. This is broadly stated to be the case by
several American physicians ; and the advantageous use
of the active principles of the sweetbread, or pancreas,
in helping the pepsin of the gastric juice in the stomach,
is vouched for by a chemist of high standing in New
York. My inquiries somewhat corroborate these views,
but in carrying out the trials I was for a time altogether
foiled in the endeavour to obtain in a convenient form
that portion of the pancreatic juice which should consti-
tute reliable pancreatin.

I could purchase useful pepsin, at a high price it is
true ; and concordant results were obtained of its powers
of solution, even if the peptic solvent was almost
invariably below a fair standard. The pancreatin sold
at the shops, either as a powder or in a suspended state
in oil, proved, on the other hand, so unequal in its action
as to disturb all parity of experiment. If I had been
dependent upon any of the samples of prepared pancreatin
I was able to procure from our best known English

10 THE DIGESTION AND ASSIMILATION OF

druggists, I should have been compelled to relinquish all
further research, not only as to its supplementary action
to pepsin, but in regard to its own specific functions.

Yery little can be said in excuse for the manufacturers
of the so-called pancreatin, who put forward, as the true
active principle* of the pancreatic juice, preparations
which rarely contain one-tenth part of the active principles
to be found in the solid contents of that fluid. But what
can be the word which will express the confidence in the
want of knowledge of patients and want of testing by
prescribers, or the unconsciousness of their own ignorance,
which permits the sale of preparations termed pancreatin
yielding less than 2 per cent, of any active principle of
the fluid, and in some instances show none whatever?
These last and utterly worthless samples have been more
frequently sent to me than the unreliable preparations
first alluded to, which do contain just sufficient of the
active principles to cover the inertness of more than nine-
tenths of their bulk.

At the outset, however, I determined to rely only on
preparations made with my own hands; the hindrance
occasioned by the bad pancreatin supplied from the shops
was so far fortunate, inasmuch as it induced me to imme-
diately devote a special attention to these experiments,
instead of proceeding with them merely as supplemental
to those commenced on pepsin.

Description of some of the Reactions and Functions of
Pancreatic Fluid.

We could scarcely expect very close accord in the
earlier observations respecting the reactions of the pan-

* It is noticeable that " the active principle" is always printed on
the labels of the preparations in the singular.

FAT IN THE HUMAN BODY, 11

creatic fluid. At a period of scientific research, J owever
brilliant, when the dispute "raged furious" be^re the
savants could decide the nature of th gastric ac :.';••, it is
not surprising to find the pancreatic mice desc"' bed as
acid, acid-saline, neutral, faintly alkali '.u\ and . trongly
alkaline. De la Boe and De Graf sta>:- it w?v- acid to
their tests and saline to their taste: Peel Jin an.i Brunner
compared the reaction to that of a neutral kait: Meyer
discovered the fluid from the pancreatic gland of a cat
to be faintly alkaline, which was corroborated by
Magendie. Tiedemann and Gmelin, taking the first
portion of fluid issuing from the pancreatic duct of a dog,
which was opened for the experiment, found it to be
slightly red and turbid ; it was put aside without testing
for some time. The next portion was whiter, with a
bluish cast, and was decidedly alkaline, being con-
sidered the unmixed fluid from the gland. On reverting
to the first portion, the test paper showed distinct acidity.

Baron Lucicn Corvisart, the eminent medical adviser of
the late Emperor of the French, referring to the previous
experiments of Pappenheim, asserts that in one of ita
functions, namely, its digestion of fibrinous albuminoid
matter, the action proceeds whether the fluid is in an
acid, neutral, or alkaline condition.

With all the apparent contrariety of the reactions thus
recorded, Corvisart's experiments are mot sufficiently
conclusive to hold good with regard to the reactions proper
to the other functions of the pancreatic fluid. Leuret
| and Laasaigne, however, afforded the first reasonable
explanation of the former seeming inconsistencies of re-
al by proving that, when freshly exuding at the
A of intestinal digestion, the fluid is always strongly
alkaline in health : that shortly after its escape into

12 THE DIGESTION AND ASSIMILATION OF

any receptacle not protected from the air it becomes
neutral, and after some time it turns acid.

Notwithstanding the valuable experiments of Bernard
during the lengthy investigations he has bestowed on the
subject, I propose to tread on almost virgin ground in
the endeavour to identify with each peculiar function
of the pancreatic fluid the characteristic reaction most
suitable for the development of its activity.

In as few words as possible, I will give a short account
of the different functions displayed by the combined
principles contained in this complex digestive.

Bouchardat and Sandras demonstrated that raw starch,
which remained untransformed in its passage through
the gizzards of birds, and through the stomachs of those
animals where the saliva is insufficient to change all the
starch swallowed, is powerfully acted on in the intestine
as soon as it is in contact with the pancreatic fluid. The
corpuscles are eroded, dissolved, and transformed into
sugar. Such digestion and chemical change involves the
hydration of the starch by its taking up an exact
equivalent of water ; this is proved in the artificial action
on starch by the pure active principle of the pancreatin
when it is separated from its congeners, glucose being tlr
result.

I find, when working with the pure principle o^
pancreatin which transforms starch, this action m
favoured by distinct alkalinity at first, passing by!
degrees through the two other stages of neutrality and
acidity. Sugar is formed out of the starch from the very!
first, and if the artificial transformation is conducted at a
low temperature, not much above 65°, by the time the
fluid becomes decidedly acid the chemical change will be
effected without putrefactive decomposition. A heat

FAT IN THE HUMAN BODY. 13

e(}ual to that of the body, when the pancreatic sugar-
arming principle is not accompanied by antiseptics
s.milar to those furnished by the gastric fluids and the
■jile, causes too rapid a change from alkalinity to strong
cidity to convert the whole of the starch, before it
.evelops large quantities of lactic acid, and putrefactive
<//;sorganization sets in.
I My experiments included the use of many antiseptics
to simulate in the laboratory the processes of nature in
^he living body. The result of employing the stronger
/'antiseptics, in quantities sufficient to prevent putrefaction,
(was, I found, equally fatal to the active principles!
(Those of a lesser astringency, with certain exceptions,
'proved themselves less competent to delay putrescence
'than to arrest the functional power of the pancreatic
principle. No foreign antiseptic enabled me to dispense
with the natural preservatives of the bile and gastric
fluids ; but with these, or rather with a portion of these,
as I shall hereafter explain, I obtained the transforma-
tions by the proper principles of the pancreatic juice at
temperatures approaching that of the living body, and
without putrefactive evidence.

The peculiar principle of pancreatin, exercising diges-
tion al power over nitrogenous substances, comports with
the functions previously noticed by Corvisart, except
that this principle, when separately used, instead of
taking the concrete fluid for the purpose, is infinitely
more energetic in a state of acidity.

Two special digestive actions of pancreatic juice having
been separately watched in their somewhat opposite
capacities, and the reactions most suitable to each
individual principle ascertained, a third, by far the most
essential of all the specific functions of the fluid secreted

U THE DIGESTION AND ASSIMILATION OF

by the pancreas, remains for investigation, namely, (
principle effecting the digestion of fat and oi]

As this portion of the pancreatic jnice has not he
tofore been even indicated, although its presence
acknowledged at all hands, and as It forms he ma
subject of this treatise, I mnst leave to the narration
my experiments snch description as may be the o{
come of long-continued labonr to advance this subject

Before entermg npon detail, it is essential to be umh
tood that, when I have nsed the word pancreatin, I ha
so designated the combination of active princip es co
tamed in the pancreatic flnid, which may be presented
a dry bnt perfectly solnhle form. Theword^nT toe
obee .enable, as it appears to refer to some sT„!

at least three dnferent active agents, each performin
distinct and even opposite functions. The taJp^S

mafterSr'^r^, " ^^/pancrea
matters soluble n water, insoluble in alcohol, and coaffu
lablc by heat, that it must still do duty for the crud
aohds of the pancreatic fluid, which ha™ been dr e
without mjury to their solubility or digestional action

Analytical Processes for the Separction of the Active
Principles and other Components.
Keviewing the causes which in all probability contribute
to render the pancreatin of the shops so poo/a digestive
^occurred to me that the fluid taken in L first Lt2
may not have been procured when the glands were

secreting strong solvent principles. Several efpenW,7terc
have remarted that the max.mum P enters

of the pancreatic juice can only he acquired by rem vhig
the pancreas of smtable animals immediately after deatff

FAT IN THE HUMAN BODY. 15

when digestion of food containing fat has commenced
from three to seven hours previously. My own experience
points to the superiority of the fluid obtained as it flows
through the pancreatic duct at that period of digestion,
but I found in practice a larger quantity is at once drawn
from the gland, taken during vigorous digestion, if it is
instantly subjected to maceration.

Difficulties were thrown in my way by the butchers
and slaughtermen to whom I applied for sweet! >i
from the animals under the necessary conditions. I was
assured that all the pigs, calves, and other beasts killed
for food are previously fasted so long that the upper
intestines are always empty. This is regarded as of
great importance by the butchers ; but as, when fasting,
the pancreatic glands only furnish fluids yielding the
smallest proportion of active principles, the scruples of
the slaughtermen had to be overcome.

At length I succeeded in procuring an occasional porcine
pancreas, which I could depend upon being extracted
from the carcase as I desired, but it could only be relied
on in this respect when the chyle in the intestine was
verified by ocular demonstration.

The pancreatic glands were passed through one of
Nye's masticating machines until effectually pulped ;
this magma being exhausted by successive washings
with distilled water at 40° F., was filtered at that
temperature to prevent the least decomposition. The
natural healthy secretion, as it flows through the
pancreatic duct, contains about 9 per cent, of solids.
These are composed of albuminoid mutter soluble in wate ',
albuminoid matter not soluble in alcohol, fatty matter,
extractive matters and salts soluble in alcohol, together
with other salts, chiefly of sodi in. All these couip<>>

16 THE DIGESTION AND ASSIMILATION OP

were found in the pancreas, the fatty constituent being
immensely larger than in the exuding fluid. The watery
extract was then subjected to several methods of analysis
to separate, as far as possible, not only the constituents
named, but to attempt the isolation of the various active
principles.

Organic matter dissolved in the watery extract is
largely precipitable by alcohol, and to that extent, while
retained in solution, is exceptionally liable to putrefy at
temperatures above 40°. In this respect it resembles in
a major degree some of the extractives of the saliva, but
this unstable condition marks an essential divergence
from the extractives of the gastric juice, which seem
always combined in their first watery solution with an
antiseptic which preserves them.

Such nitrogenous matter as is thrown down by strong
alcohol resembles albumin us substance in composition.
That which remains when the alcoholic solution aftei
filtration is evaporated, and the residue washed withl,
ether, is a pale yellow curdy substance.

Still more minute subdivision can be effected by
other and more complex methods of precipitation ; after
which, the matters separated, though consisting of or
containing the true active principles of the original fluid,
can only be allied to ordinary albuminoid matter, as they
do not react with most of the common tests for albumin.

Some of the more advanced foreign chemists have
proposed several systems of very delicate separations, by
which they claim to have produced two of the active
principles of the pancreatic fluid, each being of great
purity. The descriptions of the reactions said to accom-
plish these results having been submitted to me only by
notes, certain discrepancies and a semblance of contra-

FAT IN THE HUMAN BODY. 17

diction, so conveyed, might be removed, and the precise
modus operandi rendered clearer if more minute details
were afforded.

Acknowledging the advantage of having other minds
working with the same object, I have not hesitated to
modify the suggestions as they came to me, when in
following them to the" best of my ability I have not met
with the expected results.

The aqueous solution of pure pancreatic fluid should be
taken while strongly alkaline ; or if the watery extract is
filtered from the pancreas, the gland may be previously
rubbed up with magnesium carbonate, to over-neutralize
any acidity liable to be acquired during the long time
necessary for the extract to pass through the filter paper.
Into this, as my correspondent states, "the transparent
colourless jelly, produced by mixing nitric acid sp. g. 1*5
with starch, is thrown. The instant it reaches the
aqueous extract a white insoluble precipitate is formed,
carrying down with it the active principle which digests
fibrinous matter.'' The solution can then be filtered off,
and the insoluble precipitate redissolved in weak nitric
acid, leaving the active principle pure." The possibility
of success by this method evidently depends upon the
correctness of the assertion that the principle carried
down in the precipitate is unaffected by nitric acid.

'treating the aqueous extract in the same way, I sjib-
Ktituted for the nitrated starch a solution of the less
highly nitrated pyroxylin in ether-alcohol, which, while
precipitating out with it the fibrin-digestive principle of
pancreatin, leaves the starch-transforming agent in the

* The peculiar principle of the pancreatin fluid which digests nitro-
genous matter ia proportionally far more energetic in dissolving fibrin
albumin.

13 THE DIGESTION AND ASSIMILATION OF

solution. This may be filtered off, and evaporated at a
low temperature. The latter separation produces with
certainty an almost colourless powder, absolutely inert
as a solvent of fibrin, but a powerful starch converter.
I greatly prefer the use of pyroxylin for the isolation of
this particular principle, for I must confess I failed to
reach this result by means of the nitrated starch.

If this method of analysis can be extended by redis-
solving the double precipitate, so that the fibrin-solvent
is obtainable from a mixture of ether and water, it
will greatly add to the value of the process, supposing we
need not depend upon excessive nicety of manipulation.
According to my own experience, however, I prefer ex-
tracting the fibrin-solvent free from the starch -transform-
ing principle and all other extraneous matter by pre-
cipitating with calcic phosphate, which can be readily
conducted with the necessary accuracy.

A naturally neutral watery extract should be taken
from the gland ; that is to say, the usual alkaline extract
is allowed to stand until it has become exactly neutral.
Sufficient tri-basic phosphoric acid is thrown in to make
up the whole to a solution of one in twenty. It is then
slightly over-neutralized with a known quantity of lime
in water ; to which the precise equivalent of phosphoric
acid is added to produce an insoluble bi-calcic phos-
phate, from which the fibrin-solvent can be washed with
distilled water.

Other methods of isolating these two active principles
give results similar in all essentials to the solvents
yielded by the foregoing analytical processes. The sub-
stantial truth of the propositions involved is thus con-
firmed, and we can now class these peculiar agents and
their reactions as known principles, producing well-defined

FAT IN THE HUMAN BODY. 19

and characteristic organic change in those matters which
are appropriate to each, and in no other kind of matter.

Recent research abroad appears to corroborate the
earlier determinations of these experiments, but respecting
the exact nature of the stimulating action possessed by
such principles in effecting organic change, no general
consensus of scientific conviction is jet attained. My
endeavour is to deal with this portion of my subject as
tentatively as possible ; discriminating as far as may be
between assumed facts, credible theories, and the uncer-
tainties of both. My most important results must be
regarded to some extent by the light which can be thus
afforded ; it is therefore essential to their explanation.

The Fermentative Nature of the Pancreatic Principles.

The stimulating action of the principles contained in
the pancreatic fluid, as well as in all the other digestive
Excretions, is due to true fermentations produced by

em. These ferments must not, however, be considered

Ki strictly analogous to the alcoholic ferment of yeast ;
1 the contrary, we must try to discern the extent to
ihich their fermentative action differs from the better
fnown, and therefore more widely acknowledged, fer-
nents, so elaborately classified and described by Pasteur.
To illustrate more clearly the character of the fer-
ments forming the active principles of the pancreatic
md other digestive fluids, to those who have not made
a special study of the wonderful phenomena attending
upon the simplest and best known fermentation, namely,
Icoholic, I will explain the immediate connection
en the fermentation by yeast and the fermentation
by digestive principles.

06 sugar is not fermentable aa long as it retains

20 THE DIGESTION AND ASSIMILATION OF

its composition is such — vide the text-books. Before it
can be acted upon by yeast so as to be converted into
alcohol and carbonic acid, a preliminary change must be
first induced; this is effected when the cane sugar
becomes hydrated and its composition is found to be
made up of glucose (grape sugar) and lsevulose (unerys-
tallizable sugar). The reagent producing this pre-
liminary change was discovered by Berthelot in the
water in which yeast has been washed, even after it
has been filtered perfectly 'free from any yeast cells.
From its peculiar action on cane sugar, it was termed
inversive ferment ; and Bechamp afterwards proved that
it consists of soluble nitrogenous matter, either extracted
from the yeast cells during their growth and repro-
duction, or excreted and thrown off in the process of
their development.

The most remarkable characteristic of this soluble
nitrogenous matter is the extraordinary rapidity with
which a very minute quantity of it in solution causes
the hydration of cans sugar. The peculiarity is strik-,,
ingly indicated by all the soluble nitrogenous fermenfej
principles excreted by the digestive organs; infinitely
small quantities producing the most important and!
prolonged reactions.

The same fermentative hydration splits up cane sugar'
into glucose and uncrystallizable sugar, converts starch
into glucose and dextrin ; and the glycerides (fatty
matters) become hydrated when split up into glycerin
and fatty acids in the presence of water. The group of
different albuminoid substances which composes the
complex soluble nitrogenous ferments may also be re-
garded as the result of the breaking up of ordinary
albumin by hydration. In this essential splitting up of \ft

FAT IN THE HUMAN BODY. 21

the various constituents of food, and in their consequent
hydration, we observe the true action of the inversive,
soluble, and digestive ferments.

Whether the inversive soluble ferment be taken from
yeast-washing, or any of the digestive ferment principles
are isolated from the other constituents of the digestive
juices, all soluble ferments are produced directly from the
living organism. As long as the yeast plant lives, the
inversive ferment is freely given off in solution, except
when the presence of special antiseptics arrests this
excretion without killing the plant. Similarly, the
digestive glands of the animal body may secrete fluids
in which the soluble ferments arc rendered inert during
the period they are under the influence of counteracting
agents.

Boric acid at a certain strength of solution arrests the
vitality of inversive ferment and causes digestive fer-
ments to remain dormant until they are washed free
from its control. Alcohol has the same effect, varying
only with the amount of its dilution. Citric, tartaric,
acetic and many other acids, usually found in a dilute
form in food, exert a very injurious effect upon the
digestive ferments, if they mix with the digestive fluids
while too concentrated or in excessive quantities.

Some volatile oils, on the other hand, exercise very little
subduing influence on the solvent powers of the digestive
ferments, although many of them, especially the turpenes
(represented by oil of cloves, lemon peel, etc.), are highly
antiseptic in the prevention of putrefactive decom-
position. The volatile oils, which are themselves the
product of fermentation, appear rather to stimulate
digestion ; of this we have a good example in the volatile
principle of mustard.

22 THE DIGESTION AND ASSIMILATION OF

A wide line of demarcation is thus revealed between
the direct ferments, complete in their own organism, like
yeast, and the indirect soluble ferments which are the
product of organism but are not so organized in them-
selves as to permit of reproduction ; and this is evidenced
by the opposite reactions produced upon the two different
classes of ferments by the antiseptics enumerated.

The Emulsifying Power of the Pancreatic Fluid.

Bernard was enabled to demonstrate that no othei
fluid secreted in the digestive organs, except that from
the pancreas, can produce the complete digestion of a
sufficiency of fats or oils. The remarkable property of
forming an emulsion by mechanically holding the fat
or oil in minute globules, with water filling up the
interstices, is almost alone possessed by this juice. I
am desirous of making an amendment to M. Bernard's
statement that the power of emulsion is altogether
peculiar to the pancreatic fluid, because I find that it is
also produced to a very much smaller extent by the
saliva. I am, however, completely in accord with the
observation that the after saponification is only at present
provable when oils or fats are subjected to the digestive
fluids of the duodenum. Without refining too much on
the possibility of a similar function perhaps appertaining
to the saliva, it is evident that, as a very slight saponi-
fying action is supposed to assist in conducting the fats
of food through the walls of the absorbents, a still more
minute agency of the same description may exist in the
saliva without our being able to perceive it.

The state of emulsion is beautifully apparent if a drop
from a sample of milk is placed upon the stage of the
microscope. The globules are found floating about in

FAT IN THE HUMAN BODY. 23

that constant and rapid motion which takes place in all
similar matters devoid of organization, and is denominated
the Brownian movement. Without doubt, this movement
in the globules is essential to the persistence of a mere
mechanical emulsion; and although Mitscherlich and
Moleschott were able to show that, in milk, this emulsive
form is maintained by each globule of fat being coated
with a thin pellicle of albumin, I have noticed the larger
globules of butter, or those exceeding 2?V <Jtn °f an mcn m
diameter, have a strong tendency to aggregate, on long
keeping, by the rupture of their albuminoid vesicles.

The Brownian movement is not so manifest in the
emulsion of the fats of food formed by the digestive fluids
in the intestine, but the globules are even smaller than
in milk. Emulsions are also sometimes formed which
certainly do not contain any appreciable quantity of
albumin, and these retain their form as long as others
containing even a good deal of albuminose.

What is the peculiar principle, conveyed in the
/pancreatic fluid, which has so powerful an emulsive
action ? To this I can only reply that I have repeatedly
: found pancreatic fluid which both converted starch into
/ glucose, and fibrin into peptone, but was extremely inert
in the digestion of fat. In these cases, I have invariably
noticed that the pancreatic glands were deficient in the
( very peculiar fatty constituents of which they are so
I largely composed when taken from a healthy animal.
The inference deducible from this fact is that the
ferment prinr-iple producing instantaneous and perma-
nent emulsion in the fata of food, is itself of a fatty
. or is carried by or dissolved in fat or oil.
le other experiment corroborates this assumption,
, .lamely, if we take the other pure principles of the

24 THE DIGESTION AND ASSIMILATION OF

fluid absolutely free from fat, we find the wonderfully
vigorous emulsifying property is almost destroyed.

A great misconception as to the real characteristics of
a true pancreatic emulsion has been entertained by many,
and but few appear to have studied the different aspects
presented by such an emulsion a3 is produced on fat by
the energetic action of pure soluble pancreatin, as con-
trasted with the coarse mechanical mixtures of oil or fat
and water which are commonly supposed to represent this
function of fermentative digestion.

Some seem to think that if a bottle of oil is shaken up
with the compounds sold as the active principle of the
pancreas, and a yellowish cloud is diffused for a time
through the oil, an emulsion has been obtained. So it has,
but not the true pancreatic emulsion, which forms an
integral portion of the process by which fats are digested
and assimilated. From the unvarying result of many
hundred trials with the pure, active principles of healthy
pancreatic fluid, taken at the time of digestion, I am
perfectly convinced that no valuable result has been
attained unless the emulsion formed is as highly refrac-
tive of light as milk. The colour may vary, according to
the oil or fat used, from a far whiter fluid than the
densest milk to the opacity and colour of Devonshire
cream ; but unless at least the equivalent of the density
of the best milk is produced in oil, when a third of water
is held in suspension, no real pancreatic emulsion has
been formed.

The mere mechanical mixture formed by common
pancreatin is rarely better or more persistent than may
be produced by rubbing up oil or fat with a solution of
mucilage, or by a warm application of dissolved gelatin
shaken with oil until it becomes cold.

FAT IN THE HUMAN BODY. 25

The first essential towards the digestion of fat or oils
in the human body is that it shall assume the state of the
very finest and most permanent emulsion, and this is only
known to be attained when the oil and water is perfectly
opaque, from the minuteness of the globules. This is
the first function of the pancreatic emulsifying principle,
and by this alone can we be certain that it possesses its
proper fermentative activity.

The Manner in which a JVeio Principle is thought to
have been Detected and Confirmed.

Proceeding systematically in the examination of the
various separate ferment principles given out by the
healthy pancreatic gland, when in the greatest activity, I
arrived at the unavoidable conclusion that the reaction
proper to the exercise of all their functions in combina-
tion is that of alkalinity. The alkaline fluid produces
the perfection of emulsion described, but no chemical
change is effected in the fatty matters of food by the
pancreatic fluid alone, except after a lapse of time which
it is inconsistent to suppose can be accorded in the
intestine. Bernard believed that the slight saponification
is perhaps commenced in the intestine, and then con-
tinued in the after processes of absorption. This latter
proposition is not borne out by my experiments ; the fat
in contact with the pancreatic fluid, the bile, and
intestinal juices in the bowel, being more evidently
: lined than the oil in the villi, the lacteals, or in the
blood. How far this may bo assisted by the alkalies and
other reagents of the bile and fluids from the intestinal
jlands, I will not wait here to discuss ; merely recording
,eIny persuasion that the reactions induced by their means

36 THE DIGESTION AND ASSIMILATION OF

are of the very essence of the digestion al changes of fat
which enable it to be absorbed.

My attention being engaged more particularly in
separating the principles and in identifying their peculiar
functions, I had only arrived at the negative result before
mentioned — namely, that the further chemical change of
the fatty emulsion is probably not due to the pancreatic
fluid alone — when, in manipulating the pancreas of a pig,
I almost stumbled on what appeared to me a startling
discovery.

After obtaining the watery extract from the gland, the
strongest alcohol (not absolute) was added to precipitate
the coagulable albumin. When this was poured off and
evaporated, I found a peculiar greasy deposit. At first,
I was disposed to attribute this to the fineness of the
emulsion of fatty substance permitting it to pass through
the filter paper; but on repeating the experiment, I
obtained an almost bright filtrate of the aqueous solution,
and the alcoholic extract became perfectly clear and
brilliant. The deposit of grease was evidently not due
to the fineness of emulsion, for the finer the particles
of fat, the more opaque the milkiness would appear. I
therefore treated the deposit with ether, carbon-
disulphide, light spirit of petroleum, and other solvents
of fats and oils.

Every successive test showed the ease with which the
fatty portion was taken up by these menstrua, precluding
the possibility of its being mainly composed of the
glycerin liberated by the saponification of the fixed
f.itty acids forming the fat of the food previously given
i the pig.

When I first saw the pig, it had been fasted for forty- ,
eight hours ; a meal of boiled potatoes mixed with beef

FAT IN THE HUMAN BODY.

6uet was then given. Six hours afterwards the pig was
killed, and the pancreas submitted to the processes
alluded to. Yet here was a considerable quantity of a
brownish oil, to some extent volatile, or at least diffusible
at temperatures very little exceeding that of the body.
Extremely soluble in a very small proportion of ether, it
combined with the hydrates of sodium and potassium at
the higher degrees of animal heat — a result worthy of
note, as I am not aware of any previously known con-
dition of change in the fixed fatty acids which produces
soap at less than 176° F.

Control over the feeding of the pig for a period of
fifty-four hours appears adequate to assure us that the
glycerides of fatty acids, volatile at an animal heat,
were not contained in the immediate constituents of the
food recently given.

Absolute proof of this was desirable; so a portion of
the same sample of suet was taken, treated with potas-
sium hydrate and alcohol, and yielded a perfectly
bright solution of soap. It was then decomposed with
a mixture of hydrochloric and lactic acids, these being
found in the stomach of the pig. After well washing with
boiling water and drying in vacuo, 95*6 per cent, of
I fatty acids remained, leaving, if the due proportion
of glycerin be reckoned, no room for any trace of gly-
cerides of volatile fatty acids in the suet before the pig
ate it.

The obvious conclusion to be drawn from this extra-
ordinary result is that the animal digestion of fats and
oils' renders a certain portion of the fixed fatty acids
soluble in water and alcohol, and in a mixture of both.
If* this is correct, as is attested by all my after experi-
.to, the process of absorption of fat through the

28 THE DIGESTION AND ASSIMILATION OF

membranes of the villi of the intestines and the other
absorbents is capable of another explanation besides
that doubtfully assigned to the slight saponification also
observed.

As a short summary of the results of these preliminary
experiments, I may state : —

Firstly, that the formation of even the most perfect
emulsion of fat or oil with water does not of itself
render any portion of the oil or fat soluble in water, nor
does the fat or oil take up any water, except mechanic-
ally, to become, so to term it, hydrated.

Secondly, the addition of alkalies to fixed oils or fats at
common temperatures, whether the alkalies are as hydrates
or salts, does not affect such transformation.

Thirdly, mixtures of fixed oils or fats with water and
the solids of the pancreatic fluid, when kept for long-
periods, promote the separation of the fatty acids from
the glycerin. This decomposition is, however, effected
by that most disgusting butyric fermentation, which is
set up in the presence of putrefying nitrogeneous matters
supplied by crude pancreatin, and is never found in a
healthy state.

Fourthly, saponification is not the only natural solu-
tion of fatty matters in water at the temperature of the
body.

Fifthly, that fatty matters are found in the pan-
creatic fluid and in the pancreas in a free state; in
solution with water (hydrated); and are also slightly
saponified in the intestine. These, or some of these
different forms of fat, are distinguishable in combinations
of various proportions in the intestine, the pancreatic
gland, the thoracic duct, and while the fat or oilj is.
passing through the walls of the absorbents.

FAT IN THE HUMAN BODT. 29

OHAPTEE IT.

A BLIGHT SKETCH OF THE PHYSIOLOGY AND CHEMISTHY RELATING TO
THE PBELIMINAHY DIGESTION OF FATS.

When fat or oil is taken in food or with food, as I am
led by the whole course of these investigations to believe
it always should be, the first introductory step towards
its digestion is effected in the mouth by all animals
possessing the instinct to thoroughly masticate their
food. I am aware that this is contrary to the generally
received teaching, which only acknowledges the chemi-
cally digestive action of the saliva on starch. In a
subsidiary degree, the valuable results of good masti-
cation are admitted, so far as appertains to the preparation
of the nitrogenous portion of food for the stomach. I
wish to claim the possibility of something more than this
being effected during the chewing, mixing, and incorpo-
rating to which the separate fatty matters taken in an
ordinary meal are subjected prior to being swallowed.
The presence of the alkaline fermenta of the saliva pro-
duces a coarse emulsion, which, when the other portions of
food are easy of chymification, is not altogether destroyed
_by the action of healthy gastric juice. Observations
founded upon experiments with dogs do not enable this
to be properly shown, as these animals seldom masticate
food of this character.

Many years ago, Dr. Wright announced that the degree
of alkalinity of the saliva during digeHtion was in direct
proportion to the acidity of the stomach fluids. Of the
precise accuracy of this I am by no means convince I,
although I niust endorse JJr. Bence Jones's observation

30 THE DIGESTION AND ASSIMILATION CF

that, during the excretion of acid in the stomachic diges-
tion, the alkalinity of the other fluids is increased. I
take it that this means the total alkalinity of all the
other fluids is increased to the extent of the acid with-
drawn from them by the local digestion in the stomach.

The variation of acidity in the gastric fluid certainly
produces a marked difference in the appearance iu the
stomach. In the case of a meal containing hard, indiges-
tible, or irritating matters, the peptic solvents are found
highly charged with acid, and in the absence of sufficient
saliva, the fatty substances are seen separated from the
chyme, but pass through the pylorus at the same time in
a melted or oily form.* If the other components of the
meal are easy of chymifieation, the emulsion of fat by a
full quantity of healthy saliva is generally sufficiently
maintained against the feebler acids which are furnished
by the stomach to undertake the lighter task of trans-
forming the freely digestible albuminoids into peptones.

Fats or oils taken into the stomach without any other
food are usually swallowed rapidly ; they are, therefore,
less acted on by the saliva. The after flow of saliva
is also less abundant; this may result from the absence
of the muscular play upon the glands incident to the
masticatory action, or from the want of that sympathy
which, excites the outpour of this fluid after the savour
of the other principles of food has been appreciated by
the palate. Be this as it may, fatty matters or oils, taken
by themselves into the empty stomach, are less emulsified
by the ptyalin of the saliva and the oral mucus, and
are more distinctly separated by the'Stomach juices than

* When the acidity of the stomach is provoked to excess, no amount
of alkalinity which can be conveyed by the saliva will obviate the
separation of the fats.

FAT IN THE HUMAN 30DT. 31

when they form part of mixed meals. In the same way,
the peculiar emulsionary function of pancreatin is ren-
dered nugatory when oil or fat is not accompanied with
other 6olid food. A fully pancreatized oil or fat may
sometimes pass through the stomach by itself without
being thrown out of emulsion, and in this form, if there
is a normal flow of bile, it may be, and probably is, ren-
dered easier of digestion. The reactions of the stomach
juices are, however, almost invariably acid enough to
separate the oil from the emulsion if no other food is
present to absorb the gastric fluids.

By tying the pylorus before any portion of the mixed
contents of the stomach can pass through, the progress of
chymification and stomachic digestion may be watched
with advantage. The pultaceous mass is not found to
be uniformly acid, neutral, or alkaline. For the first
hour or more, different portions exhibit these several
conditions. Neither the flow of alkaline saliva nor of
acid gastric juice is altogether continuous, observation
lending to the conclusion that their influence on some of
the food in the stomach is frequently alternative. The
maintenance of fatty evulsion, however, depends almost
entirely upon the alkalinity retained in it being at least
equivalent +o any acidity with which it comes in contact.

After fasting for forty-eight hours, fat or oil may be
kept in the stomach for several hours by closing the
pyloric orifice, without any increase being found in the
of fat usually contained by the surrounding lym-
phatics. The addition of a very small quantity of bile
and pancreatic juice to the fat in the stomach, however,
enriches the lymph taken from the thoracic duct in the
tice of chyle, until it yields nearly one per cent, of
fattv and other matters soluble in ether.

32 THE DIGESTION AND ASSIMILATION OF

This would appear to show that a very limited but
rapid digestion of fat may, under certain circumstances,
take place in the stomach, and that it may be absorbed
there and enter directly into the circulation. The pro-
bable capacity of the lymphatics for carrying fat may
perhaps be claimed from the comparative analysis I was
enabled to make of the vascular glands of two hedgehogs ;
one killed just before hibernation, the other being re-
served until after that period. Both were of the same
age, and as nearly as possible of a size. The thymus
and appended fat glands, connected only with the blood
vessels and lymphatics, and with no direct communication
with the lacteals, became literally overcharged with fat
before the winter sleep, and 67 per cent, of fat in the
dried substance was extracted with ether. Whereas,
after hibernation, only a bare trace of fat was discover-
able in the similar glands of the sleeper when first
awakened by the approach of spring.

The distribution of fat by the lymphatic system, if this
can be admitted, affords a slight clue towards assisting
our comprehension of certain otherwise unaccountable
physiological facts. •

It is well known that the body of a well-nourished
adult contains nearly one-fourth of its weight of fat.
Equally well ascertained is the chemical truth that the
entire blood in circulation does not yield one-thousandth
part of the fatty components of such a body.* The
natural inference would therefore be that the elimination,
use, and waste in the human economy of life must be
particularly slow and small in quantity. The exact
reverse is, however, the case, as in starvation or wasting

* A man of eleven stone should have about 28 lbs. of fat and 12 lbs.
of blood in Ms body, which contains about $ oz. of fat.

FAT EN THE HUMAN BODY. 33

of the bodily tissues, the -whole of the fatty structures are
reduced more rapidly and to a greater extent than in any
of the other tissues or juices.

Before death from want of food occurs, as much as 90
per cent, of the bodily fat is starved out; and it is a
noteworthy corollary to observe that, next to the fatty
tissues, the pancreas, salivatory, vascular, and other glands
lose the largest proportion of their substance, namely, 86
per cent., from the same cause ; these include the whole
of the fat-storing and digesting organs.

If it is difficult to understand how the blood can convey
all the fatty matters to their destinations so as to supply
the large and rapid daily waste, is it not feasible to believe
that the direct circulation of the blood may be supple-
mented by the fat-carrying capacity of the lymphatics ?

However small the power of digesting fat in the
stomach may be, it seems likely to afford, artificially, the
most rapid means of recuperation after great wasting of
the fatty tissues ; assisting the resuscitation of functional
activity of the natural fat-digesting organs. Certainly
the main hope of nourishing the pancreatic and other
digestional glands, so that their specific powers may be
stimulated, depends upon the conveyance to these organs
of that constituent fat which they are unable to take up
for themselves.

To assist this supplementary action of the absorbents,
or, rather, to enable lymph to take up fat at all, the one
absolute necessity, apparent to me by direct experiment,
is the perfect solubility of a portion of the fat or oil in
the w tigtituent <>f the lymph, minute though it be.

Pure lymph, as we know, is quite clear and devoid of
milkiness, even to the minimum extent indicated by
opeleeoence. After fasting from food for some time, the

34 THE DIGESTION AND ASSIMILATION OF

thoracic duct contains transparent lymph only. Yet.
when the pylorus is tied, previous to a meal being given
in which fat is contained, the increase of fat to be found
in the thoracic duct does not cause, in the slightest degree,
the characteristic milkiness of chyle absorbed through the
lacteal s. In other words, this lymphatic -absorption of
fat, which is proved by analysis, consists only of fat
soluble in the watery lymph.* This leads me forward
to the consideration of the manner in which any portion
of fat becomes truly soluble in water so that it may be
absorbed.

CHAPTER III.

THE DIGESTION OF FAT IN THE SMALL INTESTINE.

We are obliged to acknowledge that, with the highest
microscopic powers, we fail to find the faintest indication
of any pores or ducts in the recognized absorbents of the
intestine. The absorption of food by blood vessels is
apparently almost omnivorous, many substances in a
sufficiently subdivided form seeming to be taken up by
them ; in addition to which, solutions and gases of most
kinds are also freely received and mingle with the blood,
frequently without being assimilated.

* I am particularly anxious to avoid laying undue stress upon the
amount of fat digestible in the stomach or capable of being- carried by
the lymphatics. The first is, I am aware, but very small, the latter
being difficult of estimation.

FAT IN THE HUMAN DODY. 35

The penetration of solid particles, such as the sharp
dust of charcoal, cannot, however, be regarded as absorp-
tion, being due to attrition forcing them mechanically
through the walls of the vessels. The true absorption of
liquids also depends upon their suitability to mix with
and afterwards form a portion of the blood ; and I have
proved by repeated experiments that no other kind of
fluid enters naturally into the circulation, although it may
be forced into it.

Fat is found in an average sample of blood to the
extent only of 1*5 per thousand, and this partly in a
soluble form and partly as serolin. Free, fixed, or uncom-
bined fat will neither mix with to form part of the blood,
nor will it in this condition pass inwards through the
walls of the vessels. A certain amount of a different kind
of fat is, however, retained in the blood, which only
becomes insoluble after exposure to the air ; this is pro-
bably excrementitious, or a residue accumulating from
the soluble fat which is precipitable from solution by
the salts of the alkaline earths, and particularly by
phosphate of lime. It resembles cholesterin, but melts
at a much lower temperature, namely, 97° F. This
peculiar fat is, 1 find, eliminated through the sebaceous
glands, as well as by the bowels.

The chief supply of fat to the blood is not by direct
absorption from the blood, but from the chyle trken up by
the lacteal*. During the active absorption of chyle
containing fat, the villi become whiter and more opaque,
and when the fat has been duly prepared by admixture
with bile, pancreatic fluid, and the juices of the Intestinal
glands, a portion of this fatty constituent may be traced
in the in pit helium. The columnar cells, here

and there, become filled with brilliant globules of oil,

36 THE DIGESTION AND ASSIMILATION OP

which I have ascertained to be free oil, containing no
water or other constituents of the chyle.

The columnar cells are so small that 1600 of them
placed end to end only measure one inch, their diameter
being less than half this size ; the value of the most per-
fect emulsion is therefore evident, by which only minute
globules are presented to the cells. But a mere me-
chanical mixture of oil and water, however finely sub-
divided for the moment, does not enable the oil to permeate
the delicate membranous walls of the cells. The experi-
ments proving this have an importance which demands
a more detailed description than my present space
permits, but I hope shortly to further particularize.

After fasting a dog for two days, a meal of beef kidney
fat was given, in which were a few pieces of old tanned
leather to excite due peristalsis. The bile and pancreatic
ducts were previously tied, and a ligature was passed
round the bowel, about two feet from the pylorus. At
the end of three hours the animal was killed, and the
condition of the intestine was examined, both microscopic-
ally and chemically, for any fat it might have absorbed.
Scarcely any oil globules were found to have entered the
cells of the villi with which the fat had been so long in
contact, and by exhaustion in boiling ether no difference
could be perceived in the amount of fat extracted from
the portion above the ligature, as compared with that
obtained from an equal weight of intestine taken from
below the part closed by tying.

A similar experiment was performed upon the intestine
of another dog, the only difference being that an alkaline
solution of pancreatin with bile extractive was mixed
with the fat before it was swallowed. A third dog was
fed as in the first case, but the natural secretions of bile

FAT IN THE HUMAN BODY. 37

and pancreatic fluid were permitted to flow into the in-
testine. In both these latter cases the fat, in an oily-
state, was found in the cells of the villi, and analysis gave
evidence of a very large absorption of fat in the parts
above the ligatures, while in those portions beneath it
no increase of fatty constituents was yielded.

These results are in themselves sufficiently conclusive,
but I have observed that they are corroborated by all I
have ascertained concerning the still more interesting
processes by which fats pass through the various mem-
branes and tissues, when suitably prepared either by
natural or artificial means. It is at the very point of
transmittance that the complex actions and reactions
occur which are included in the but little understood
digestional absorption of fat.

The moistened membranes of the villi, lacteals, and
blood vessels do not pass free fixed oil by endosmosis, as
is believed by some ; neither will mere alkalinity assist in
its absorption, as I was able to demonstrate by a fourth
experiment. The mixture of pure pancreatic fluid and
fat appears almost equally incapable of being taken up
by the absorbents, but the experiments to determine this
were not quite so conclusive, probably because we were
unable to prevent the presence of fluids from the intes-
tinal glands. Many and various supplementary ex-
aminations confirm these data, and the necessity is
plainly shown for the presence of an alkali, pancreatic
fluid possessing full fermentative vitality, and certain
elements of the bile, to render fat truly soluble in the
fluid before it can be absorbed.

A very minute portion of the soluble oil appears
sufficient to effect the transfusion of a large quantity of
a fine emulsion. It may act by rapid endosmosis, carrying

38 THE DIGESTION AND ASSIMILATION OF

with it the fixed fats, and may then return by exostosis,
having deposited the globules of free oil within the mem-
branes of the cells. By a similar action the fixed fats
may pass from one membrane to another, until it is mixed
with the ehyle in the lacteals and the blood in the
capillaries of the bowel. I am not in a position to
demonstrate that this is the precise manner in which the
soluble portion of the oil enables the other portion to be
absorbed, but I have proved that fat which contains no
soluble glycerides is not absorbed until the reactions of
the bile and pancreatic fluid have rendered a portion of
it soluble in water.

Whatever description of fat may have been eaten, it
must be so far transformed as to approach in composition
to that of butter or the fat of milk which has passed
through the mammary glands.

It may not be generally known that butter is, to a
certain extent, easily rendered soluble in water ; but as
this peculiarity affords the distinctive difference between
pure butter and the common fats with which it may be
adulterated, and as this is now relied on in butter
analysis for the detection of such adulteration, I may,
perhaps, be excused if I repeat the evidence of this
instructive fact, which first dawned upon me some three
years back.

Ordinary mutton, beef, and pork fats are composed
almost exclusively of the glycerides of the fixed fatty
acids, such as the stearic, palmitic, and oleic acids. If these
are saponified with hydrates of the alkalies, and the soap is
decomposed with a dilute acid, such fats will yield more
than 95 per cent, of the fixed fatty acids, which will float
upon the water, being absolutely insoluble in that con-
dition. If, however, butter is saponified, nearly 14 per

FJCF IN TH^ HUMAN BODY. 39

cent, of other fatty acids and glycerin are sei free ; these
are both volatile and truly soluble in pure water.

The analogy is perfect between butter and the fatty
matters of food, after they have been acted on by the bile,
pancreatic, and other essential fluids in the intestine; a
portion of the fat, varying from 4 to 7 per cent., being in
true solution by the time its digestion is complete and
it is ready for absorption. A slight saponification is evi-
dently required to form a hydrate of the fatty matters
by the fixation of a portion of water. This product is in
its turn decomposed, and the soluble fatty acids and
glycerine liberated to enter into solution. Bernard has
always maintained that soap is formed in the intestine,
and I am sure that no careful experimenter can fail to
find it during a vigorous digestion of fat ; but I diverge
from M. Bernard's views when he assumes soap, as such,
to be the vehicle — much more, as the only vehicle — for
the transfusion of fats through the various membranes.

As I before stated, I am not greatly concerned now to
adopt any dogmatic theory of the exact minutiae of such
transfusion, but I must emphatically declare that I can
find no actual soap except in the intestine, even when a
considerable quantity of soap has been injected into it.
I therefore lean strongly to the opinion that saponifica-
tion is only a preliminary process, confined to the bowel
alone. The soap, when formed, has to be split up before
its are absorbed through the several membranes so
that they may be taken up in the circulation.

The very support afforded by this possible advance
upon previous tenets enhances the practical value of the
discovery that soluble fatty matters are ossontial to the
healthy secretion of the pancreatic glands. The experi-
ments which prove that the active functions of the pan-

40 THE DIGESTION ANp ASSIMILATION" OF

creas depend chiefly, if not entirely, on its being itself
supplied with fat soluble in water, seem incidentally to
point out the conditions under which the supply can be
afforded. Having taken the subject thus far in recording
a brief generalization of my rough analytical notes, I
must reserve a few words explanatory of the attempts
made to arrive at a synthetical product complying to
some extent with these essential conditions.

CHAPTER IT.

ARTIFICIAL AIDS TO THE DIGESTION OP FATS.

All animals suffering from emaciation labour under the
same degeneration of the fat-digesting organs in varying
degrees. From whatever original causes the pancreatic
functions have lapsed into abeyance, no sufficient or
healthy flow of the digestional fluids is ever found during
wasting diseases. This is provably true of dogs, pigs,
calves, and other animals which become attenuated when
plentiful food is provided. It is not difficult to insert a
drainage tube into the pancreatic duct and test the differ-
ence of the emulsifying power of the fluids obtained on oil,
which may be compared with that produced by animals
possessing an obviously healthy digestion. A regular and
reliable flow of bile is equally essential to the formation
of soluble fat or oil, and this is as frequently found want-
ing during the digestion of food by all animals losing
weight, unless it be from over-exercise or want of proper
food.

FAT IN THE HUMAN BODY. 41

Nothing appears to restore the healthy functions of
the liver and pancreas in these cases, except the frequent
ingestion of oil or liquid fat, so treated artificially that it
is already partially transformed by fermentation and the
reaction of bile. Seized on with avidity by the absorb-
ents, it is insensibly assimilated by the digestive organs,
until they gradually become strengthened, not only to
provide their own nourishment, but to transform a suffi-
cient quantity of fat to supply the inevitable waste
throughout the body.

The fat or oil most suitable for general nourishment is
evidently that which most nearly approaches the com-
position of the fat to be renewed, but a fallacy underlies
the proposal that the small quantity necessaiy to give a
periodic impetus to the digestion of the common fats of
food need be, or indeed ought to be, of this exact com-
position.

It is admitted by those who contend for the adminis-
tration of the more solid fats as a pancreatic emulsion
that, in the first instance, oil, such as cod-liver oil, " can
be hurried most rapidly into the jpulmonanj (?) circula-
tion ; it is the fluid oleinous kind of fat that can pass by
the portal instead of by the lacteal route." It is, as Dr.
Dobell says in another place, " like water to the uprooted
flower." But, then, this candid writer proceeds to advise
the use of solid pancreatized fat, because " if you keep it
(the flower) in water after it has revived, instead of
planting it in good soil, it will droop again and die for
want of materials on which to live." There would be
great weight in this, if the fat proposed to be made into
the emulsion ie exactly of the composition of human fat,
and no other fat slvould be taken in the ordinary diet.
Dr. Dobell, however, advocates the use of a far more solid

42 THE DIGESTION AND ASSIMILATION OP

fat than human fat, and forgets that the animal fats of
food contained in his own dietary are also of this precise
nature. He also loses sight of the obvious necessity for
a due admixture of the "fluid oleinous kind of fat," to
approximate the harder fats of the diet to the normal
fatty matters of the human body. To continue his own
metaphor, the flower requires not only " good soil," but
periodic watering.

The advantage of an emulsion of the more fluid oil to
temper down the too great solidity of the other fats taken
in ordinary diet is therefore manifest. As I have proved
this to be the case with pigs, in which the lard more
nearly approaches the consistence of human fat, I think
we may assume the same to h;ld good in the human
digestion of fat.

Taking perfectly soluble pancreatin,* and completely
emulsifying a suitable oil with water (two parts to one),
I find there is a difficulty in preserving the ferment
principle from working itself out in the course of a few
days; after which the pancreatized oil will not com-
municate its emulsifying property to other fats or oils
with which it may be brought in contact, as it does when
the ferment is still in vigorous activity. Hence, we
should require a fresh preparation to be made almost
every day in summer-time, or the fatty matters of food
will not be transformed so as to be digested except by
those who do not require such assistance. To obviate
this, I made numberless experiments with temporary
antiseptics, and I conclude that one only is really suitable.
Boric acid appears to arrest any after fermentation in the

* If any portion of the pancreatin is insoluble in water, it denotes a
highly objectionable mode of preparation ; the true ferment being killed,
and the whole exceptionally liable to ammoniacal decompositior

FAT IN THE HUMAN BODY. 43

emulsion without injury to it ; and when it is combined
with the soda to represent that constituent of the bile
always forthcoming in the naturally healthy digestion of
fat or oil, I observe that the salt formed becomes so
dissolved and diluted in the digestion of food that the
pancreatic ferment resumes its activity, and all the
other tats of the meal become in a like manner trans-
formed.

At this period of liberating the ferment from the
temporary antiseptic influence of the boric acid, there is
a liability to a slight putrefactive decomposition, which is
only restrained naturally by other principles of the bile.
At first I was led to attempt this artificially, by adding
glyco-cholic acid in its original combined state (the
"crystallized bile" of Plattner), but the flavor was so
nauseous that I could not get animals to swallow oil
prepared with it. Reflecting that the pancreatin used
was from the pig, and, according to Strecker, the bile of
that animal contains glyco-cholates differing from ox
bile, I refined the glyco-hyocholic acid until the objection-
able bitterness was removed, and I was pleased to
observe that its function in the intestines was but little
impaired.

Testing oil prepared with soluble pancreatin, soda,
boric acid, together with a trace of hyocholic acid, I have
every reason to believe that a transformable modification
of the oil is reached, which is digestible in the most
atrophied condition of the organs.

All the elements for a gentle but rapid saponification
are insured, and the splitting up of the soap is favoured
by the presence of a small quantity of already hvdrated
oil in Bolution. How little of this actually soluble
glyceride of volatile fatty acids is sufficient to continue

44 THE DIGESTION AND ASSIMILATION OF

the hydration of the remaining fats during digestion is
almost impossible of estimation. I have, however, satis-
fied myself that very small proportions yield good results,
but slowly ; a larger quantity promoting extreme rapidity
of absorption.

Nearly two years of almost incessant observation
affords a fair means of judging as to the corroboration
since given by constant repetition of the more important
determinations. But the familiarity with the indications
thus acquired may inspire more confidence in the results
than might be accorded to the analogy between experi-
ments upon the lower animals and the effects of the
same kind produced in the human body. As soon, how-
ever, as the principle involved was made plain, every
opportunity was embraced of watching the direct work-
ing out of the problem, as applied to the assistance it
affords to the digestion of fat in the wasting diseases
which afflict humanity.

This more properly belongs to the science of medicine
than to that of pure physiological chemistry. I was,
therefore, fortunate in obtaining the assistance of Dr.
Drewry in elaborating the use of fatty matters con-
taining hydrated and soluble oil in cases of consump-
tion and other forms of wasting in the tissues. His
testimony as to its adaptability must speak for itself;
but some of his cases have been within my own frequent
observance, and I cannot refrain from expressing the
intense gratification it has afforded me to note the almost
immediate gain in weight and improvement of health
which has resulted, even in some of the worst instances.

FAT EN THE HUMAN BODY. 45

ADDENDUM.

EARXT EVIDENCE OF THE COMMENCEMENT OF WASTING DISEASES
DISCOVERED BY THE EXCRETION OF SOLUBLE FAT.

Urese and fcecal excreta have been frequently sub-
mitted to me for examination by members of the medical
profession, in cases where there was reason to believe
a direct loss of fatty substance occurred through the
kidneys or bowels.

In certain morbid conditions I have found free fat
or oil in the urine. It was not detected in most cases
until after cooling, when it assumed a chylous or milky
appearance. This usually happened without the presence
of any considerable quantity of albumin. In other cases
fat or oil was found which never showed itself to the eye,
and these were invariably connected with phthisis, tabes,
or nervous wasting. The quantitative estimation of
these transparent fats always presented difficulties I
could not account for. In drying the residues I
experienced a loss of weight which continued as long
as they remained in the drying chamber of the water
bath ; repeated weighing could not, therefore, be de-
pended on to confirm the absence of the solvents. Since
making the discovery of the soluble and volatile fatty
matters produced by fermentation in the intestine, this
r,pancy is explained ; and I have no doubt, from
samples more recently analyzed, that mere traces of
soluble fat in the urine may frequently mark the earlier
stages of many wasting diseases. To obtain a certain
verification of this slight excretion, vapor distillation
must be resorted to, and the most accurate manipulation

46 THE DIGESTION AND ASSIMILATION OF FAT.

is required to prevent the loss of such traces of soluble
volatile fatty matters as are sometimes to be found at the
commencement of the disease.

Similarly, I now always submit the foecal matters to
this, among other delicate tests. The result is that a
false or secondary digestion of fat is often found to have
taken place in the lower bowel without any benefit being
derived from it. On the contrary, it seems to denote one
of the first symptoms of the degeneration of the natural
fat-digesting organs. As this is of importance in point-
ing out a possibly unsuspected mischief, I have thought
attention should be directed to the means analysis affords
of confirming or removing uncertain suspicions as to such
morbid conditions. These may, or may not, be intimated
by a slight glistening film, either on the surface of the
solid excreta or floating in the urine.

Interesting as such investigations are in supplementing
the foregoing inquiries, I have had to regret the interrup-
tion lately of experiments extending over nearly seven
years. The unexpected enforcement of certain rules of
Gray's Inn has practically closed my laboratory there
for these purposes. I have, however, now made special
arrangements at my new laboratories in Duke Street,
Grosvenor Square, which will, I hope, enable me to
complete at least some of the other physiological experi-
ments, and to proceed with analyses such as have been
lately forbidden to me.

96, Queen Anne Street,

Cavendish Square.

Date Due

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Digestion and assimilation of fat

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